Radiation imaging systems for irradiating an object with radiation and imaging the radiation that has passed through the object have been widely used in dentistry, mammography and chest radiography apparatuses. For the radiation detector section, flat panel detectors (hereinafter referred to as “FPDs”) capable of converting radiation directly into digital data have been realized. FPDs are rapidly becoming widespread as they are advantageous in that the image can be checked immediately, as compared with conventional schemes where imaging plates are used.
Typical FPDs include those of the direct conversion type which use amorphous Se to convert radiation directly into an electrical signal, and those of the indirect conversion type which once convert radiation into light by means of a scintillator such as CsI:Tl and Gd2O2S:Tb, and then convert the converted light into an electrical signal by means of a photodetector such as a CCD. The direct conversion type has a problem in that a large amount of noise components is contained in the image. Therefore, at present, the indirect conversion type is used more often.
The radiation image conversion panel of an FPD is composed of a plate-shaped photoelectric converter, and a plate-shaped scintillator disposed on the photoelectric converter, for example. This radiation conversion panel has a structure in which X rays having passed through the subject impinge on the scintillator, and light generated by the scintillator is guided from the X-ray irradiation side toward the photoelectric converter side. The scintillator has a structure in which a fluorescent material is provided in the form of a plurality of fibers (hereinafter “fibrous phosphors”), which are disposed in parallel to one another, so as to guide light toward the photoelectric converter.
Patent Document No. 1 proposes a radiation image conversion panel using a combination of columnar crystals and non-columnar crystals as the plate-shaped scintillator, where the difference in refractive index between the columnar crystals and gaps therebetween is utilized to reflect light inside the columnar crystals so as to guide light to the photoelectric converter.
Also, a structure is known in the art in which a fluorescent material made of an oxide or an oxysulfide is spun into fibrous phosphors, which are bundled together with an adhesive material (Patent Document Nos. 2 and 3).